Agenda 0 Today 0 Assignment 2 Due 0 Sequence Diagrams- View & Data Layers 0 Message syntax 0 Cohesion & Coupling 0 Next Week 0 Review and wrap-up 0 Structure of the Final Test 0 Assignment No 2 Returned SheridanObject Oriented Methods1

SheridanObject Oriented Methods2

Layered Design 0 Smaller systems 0 View layer 0 Business logic layer 0 SQL statements are included in the methods of the domain classes 0 Larger systems 0 View Layer 0 Business Logic Layer 0 Data Access Layer 0 Sole responsibility is to execute database SQL statements 0 Get the results and provide the information to the business logic layer SheridanObject Oriented Methods3

Data Access Layer 0 Two ways to instantiate a Customer object in memory from a data base. 0 Approach 1 0 Using the constructor of each domain object 0 Approach 2 0 Using the data access layer object. SheridanObject Oriented Methods4

SheridanObject Oriented Methods5 Approach 1

SheridanObject Oriented Methods6 Approach 2

Example – eCommerce System Use Case: “Cancel Order” [1] SheridanObject Oriented Methods7

Example – eCommerce System Use Case: “Cancel Order” [2] SheridanObject Oriented Methods8

Example – eCommerce System Use Case: “Cancel Order” [3] Sheridan Object Oriented Methods 9

Some Fundamental Design Principles 0 Coupling 0 Measures how closely classes are linked 0 Cohesion 0 Measures the consistency of functions in a class Sheridan Object Oriented Methods10

Coupling & Cohesion - Fundamental Design Principles 0 Coupling – qualitative measure of how closely classes in a design class diagram are linked 0 Number of navigation arrows in design class diagram or messages in a sequence diagram 0 Loosely coupled – system is easier to understand and maintain 0 Cohesion – qualitative measure of consistency of functions within a single class 0 Separation of responsibility – divide low cohesive class into several highly cohesive classes 0 Highly cohesive – system is easier to understand and maintain and reuse is more likely SheridanObject Oriented Methods11